Control or regulating system employing fluid pressure



I, Pec. 4, 1945 R. H. NISBET EI'AL 4 9,

CONTROL OR REGULATING SYSTEM EMPLOYING FLUID PRESSURE Filed 061;. 2, 1941 3 Sheets-Sheet 1 65 5915968662 g1 Fig.1.

llvvavraks,

v R.H.NISBET undw. G. HARDING,

THEIR Arromysy; v

4, 1945- R. H. NISBET ETAL 2,390,119

CONTROL 0R REGULATING SYSTEM EMPLOYING FLUID PRESSURE Filed Oct. 2, 1941 s Sheets-She et 2 Fig. 1A

- llYl/ENTORS, ROBERT H. NISBET and WILLIAM G. HARDING,

jWz M T H E IR Afro/we- I Dec. 4, 1945.

- R. H. NISBET ETAL CONTROL 0R REGULATING- SY STEM EMPLOYING FLUID PRESSURE Filed on. 2, 1-541 3 Shets-Shee t a llwmms. ROBERT H. NISBET and WILLIAM G. HARDING, THEIR MM i so 61 78 39 l Patented Dec. 4, 1945 CONTROL 0R BEGULATING SYSTEM EMPLOYING FLUID PRESSURE Robert Hayes Nisbet, Stroud, and William George Harding,

Gyroscope Company Whitton, England, assignors to Sperry Incorporated. Brooklyn,

' N. Y., a corporation of New York Application October 2, 1941, Serial No. 413,317

2 Claims.

This invention relates to control and regu1at-' in8 systems of the kind in which a' primary controller controls a fluid pressure servo-motor through a relay valve, and it is concerned with the provisions of means for exerting a return action. or repeat-back, on the control system in dependence on the operation of the servo-motor, to cut 0!! further operation of the servo-motor.

- While the invention has wide applicationin vari-' ous fields, one use to which it may be put is in an automatic pilot for dirigible craft, such as aircraft.

In known forms of automatic pilot for aircraft. control is exercised from a gyroscopic device (when the craft becomes displaced from a desired attitude) by means of a cut-oi! disc or shutter connected to the gyroscope, and movable in relation to apertures in a pick-ofl member,

such movements resulting in the application oi? pneumatic pressure to a relay valve, which is thus moved and causes the transmission! of a propor- Great Britain December 23, 1940 v system there is no positive relation between the servo-motor movement (and consequently the movement of the control surface of the craft) on the one hand and the deviation oi -the craft from its desired attitude on the other. because the position of the control surface of the craft at which the relay is restored to its neutral position depends on the pneumatic pressure applied to the relay under the control-of the primary controller) relative angular movement of the pick-off device and the and this pressure depends on the cut-off gyroscope in a somewhat uncertain manner.

tional hydraulic pressure to operate a servo-motor from which a control surface or the craft is thus moved to restore the craft to the desired attitude. Various proposals have previously been made to introduce a return action or repeatback in such a system. In one proposal a pulley and wire arrangement between the servo-motor and the primary controller is designed to restore the latter to a neutral condition when the servomotor is operated. Such an arrangement is inconvenient and has other disadvantages. In another proposal a repeat-back cylinder located in the vicinity of the relay valve is connected in the flow circuit of the pressure fluid returning from the servo-motor, so that a piston in this cylinder is moved proportionally to the movements oi the servo-motor. This piston is connected to restore the primary controller to a neutral condition by moving the pick-oil device to follow the cut-oi! disc. The repeat-back cylinder and piston in this system are therefore responsive to the flow of oil into and out of the servo-motor. Since the same total volume of fluid as moves into and out of the servo-motor has also to pass into and out of the repeat-back cylinder, the latter must be at least as large as the servonnotor: it must in fact be considerably largerfthan the servomotor to allow for leakages. This renders the oil valve unit very bulky and adds considerably to the total weight of the equipment.

In yet another proposal a hydraulic pressure depending on the pressure applied to the servomotor is caused to act on the relay valve to restore it towards its neutral condition. In this by fluid pressure.

'. on the other hand. free troller adapted,-

The present invention consists in a control or regulatin system comprising a. primary conupon displacement from a neutrai condition, to like, from which a fluid pressure servo-motor is set into operation, and means which under the influence of the differential pressure the servo-motor, restore the primary controller towards its neutral condition.

It is important to distingu tem operated by fluid flow and a system operated In the rum. In a ystem operated by fluid pressure,

e of fluid is posa difference points sible and the system is operated by of pressure between tappin s at different in the fluid path. The invention provides a fluid-pressure control system having many advantages. The apparatus involved is compact and is easily installed; the system operates satisfactorily as a control for a hydraulic servo-motor with a hyaction even if there draulically operated return is air present are oil leakages and even if there in the hydraulic fluid. This last proper y from the fact that the action depends on the pressure of the fluid and not on the fluid. flow. For this last reason also his to pneumatic control as control. ,T

' The invention, which is applicable to a wide variety of control and regulating systems, will be clearly understood from the following description of forms (given, however, merely by way of example) which it may assume when applied to the automatic control of an aircraft from a gyrohcrlzon. This description will be more readily followed by reference to the accompanying drawings in which:

- Figures 1 and 1A rustic v emlargely in section, of an automatic actuate a relay valve or the applied to between a sysformer the fluid path is closed by a member movable by and with they fluid, but always preventing a free passage of results a the invention is applica-, readily as to hydraulic taken together show a sche-' v her 4 is tumed' about covered and the other covered,

control system for aircraft embodying the invention; and

Figures 2 and 2A taken together show a schematic view, largely in section, of a modification, embodying the invention, of the system shown in Figures 1 and 1A in which the repeat-back or ed for pivotal movement in the instrument case about the axis I, in such manner that this disc is stabilised against pitching of the craft. There is also provided in the instrument case of the gyro-horizon I .a follow-up frame 4,'also mounted for rotational movement about the axis I. and provided with a machined face I closely adjacent to the disc I. The follow-up member 4 constitutes the pick-off device for the gyroscope, and cooperates with the disc I to form the primary controller for controlling the elevator of the craft.

For this purpose two ports I, I are formed in the face I of the member 4, communicating with channels in the follow-up frame 4 and thence with channels in the bearing s p t! for the axis I, and thereby with the pipes I, I', the channels being so formed that communication is maintained even if the follow-up mem theaxisI. ThepipesI,I' lead into a diaphragm chamber I on opposite sides of the diaphragm II, and thence'are in communication with the atmosphere through re-, stricted ports II, II'. The interior of the casing of the gyro-horizon I is maintained at a reduced pressure, atmospheric air therefrore being sucked inthrough the ports II, II' into the diaphragm chamber I, and thence by pipes I, I to the ports Normally the ports I, I are both partly covered to substantially equal extents by the cutoif disc I, but, if the aircraft to the disc I. one of the ports I. I becomes unto a greater extent than normal. In Figure 1 port I is shown as uncovered and port I as covered, whereby the airpressure in the left hand side of the chamber I is lowered towards that of the interior'of the gyrohorizon I, andv the pressure in the right hand raised towards that at the atmosphere, so that the diaphragm is forced to the left. The diaphragm II is linked to the piston rod II of the relay valve II controlling the elevator servomotcr I4 which. is connected to operate the elevator II. In this way the gyroscope and its pickdevice constitute a for exerting control of the craft through the relay valve II. A full description of the parts so far referred to is to be Patent Specification No. 416,813.

when, as shown in Figure 1A, the diaphragm II and the piston rod are displaced to the left. the pistons I], II, II uncover the ports II, II, II and piston II lifts the washer II oi! its seating I'I against the resistance of the spring II. This spring in combination with the complementary spring II, washer II, seating I1, and piston II, thus act as a centralising mantepitches relatively.

primary controller I, I, I, I'

found in more detail in British s,sso,us

ment to restore the valve rod II and diaphragm II to their normal position in which the pistons II, II, II cover the ports II, II, II. Ports II and II are connected, by way of the channel II, to the pipe I4. Port II is connected to pipe II, port II to pipe II, and port I4 to pipe II. A pump (not shown) delivers oil under pressure to pipe II, the oil being obtained from a reservoir or sump (not shown) to which it is returned through pipe I4.

The pipes II and II lead to the opposite ends of the hydraulic servo-motor II-, pipe II being provided with a needle valve II by which the rate of fiow of oil to or from the servo-motor may be controlled.

The chambers II, II at the ends of the valve, in which are located the springs II, II, are interconnected by the passage I! through the piston rod II. The drain pipe II leading from chamber II is thus also in communication with chamber II so that oil leaking past either of the pistons II, II may drain away through it.

The operation of .the parts so far described is as follows. If the craft pitches upwards, the disc I takesup a position relative "to the follow-up membersimilar to that shown in Figure 1, so that portI is uncovered and port I covered. The diaphragm II is forced to the left taking with it the valve rod I I whereby ports II and II are put' into communication with each other through the space between the pistons II and II, and ports II and I4 are put into communication with each other through the space between pistons II and II. Oil flows in from the pump through pipe II by way of ports II and I4 into the lower end of the servo-motor I4 causing the piston to move upwards. The oil in the upper end of the servo-motor I4 is expelled through the pipe II, ports II and II, channel II. and pipe I4 to the sump. The movement of the piston of the servo-motor I4 causes the elevator IItc be deflected downwards therebycausing a force "to be applied to the craft to correct the pitch.

when the craft pitches downwards. the valve rod II is displaced in the opposite direction, port II is put into communication with port II, and port so that the servo-motor I4 and the elevator II'are operated in the opposite sense.

In order that the servo-motor I4 shall not move too far, it is necessary to provide means by which movement of the servo-motor shuts off the valve II, I I.- The present invention provides simple andconvenient means for bringing about this result.

In carrying the invention into eifect in one convenient manner there is provided in the vicinity of the valve II (and preferably forming part of the same unit as the valve) a repeat-back -cylinder II containing a piston 40 secured to a piston rod 4|. The cylinder is provided with two elongated end caps 4I, 4I and the piston rod panes through a closely fitting hole in the end cap 4I. Loosely fitting 'on the piston rod 4| are two sleeves 4I, 4I' having large flanges 44, I4

on the inner ends (adjacent to the piston II).

and smaller fianges 4|, 4|. on the outer ends.

The elongated end caps 4I, II are bored to permit :theflmedendfltomovetotheleft (asseenih Figurel) intheboreofcap4I andthe flanged end 4I' to move to the right in the bore of cap 4I' for a distance-equal to the desired stroke of the piston II. The movement of the sleeve 4I to the right, (as seen in Figure 1A) when the piston 40 is moved to the right, is limited by the engagement of the flange II with a shouldered nut 4I which is lecrewed into the end cap 42. Bin

larly the movement of the sleeve 43 to the left is limited by the engagement of the flange 45' with the shouldered nut 46. Compression coil springs 41, 41' act'betweenthe nut 46 and the flanged end 44 of the sleeve 43 and between the nut 46' and the flanged end 44' of the sleeve 43', thus keeping these sleeves forced axially inwards towards the piston 40. The nuts 46, 46' are adjusted and fixed in position so that when both the sleeves 43, 43' are forced by the springs 41,

facilitate the adjustments referred to the end cap 42' ma itself be provided with a removable screw cap 42", removal of which renders the nut 46' accessible.

If the piston 40 is moved to the right from the position shown in Figure 1, the spring 41' is compressed further but the spring 41 does not extend, as the sleeve 43 can move no farther to the right. In movement to the right the piston therefore experiences the full restoring force of the spring 41'. The magnitude of this restoring force during the initial movement of the piston is dependent on the initial compression of the spring. This initial compression is made of such value asto ensure that the initial restoring force is sufilcient to move the piston 40 and the parts operated by thepiston rod 4| against whatever friction they experience. However, all these parts are designed to keep such friction as low as possible (in particular the piston 40 is an easy fit in the'cylinder 39) so that the springs 41, 41' need only have a slight initial compression and yet will centralise the piston 40 against friction in the absence of a force causing a displacement. I The two ends of the cylinder 39 are in communication by way of the ports 48, 48 and channels 50, 5| with the pipes 3|, 33 leading to the servo-motor I4. As shown, such communication is ensured by connecting the channels 50, 5| to ports 52, 53 in the same portions of the cylinder of valve l3 as those containing the ports 22, 24. As a result, the difference of pressure effective in the servo-motor is also effective in the two halves of the cylinder 39, and the piston 40 and piston rod 4| are displaced against the springs 41, 41' through a distance proportional to this difference of pressure. The follow-up frame 4 of 'thegyroscope is operated from the piston rod 4! in the following manner: A

The follow-up frame 4 for the gyroscope is provided with a gear segment 54, which meshes with a worm 55 cut on a hollow shaft 56. Thisworm is axially slidable on-the inner co-ax-iai shaft 81, to which it is splined by the pin and slot means 58, so that the shafts 56 and 51 turn together in bearlugs 59, 59'. Bearing 59 is located in the front wall of the instrument case I while bearing 59' is located in a bushing 60 securedin, the rear wall.

The gyroscopic unit I and the unit comprising the oil valve Hi, the repeat-back cylinder 39, and,

the diaphragm chamber 9, are, as shown in Figures 1 and 1A, rigidly connected, the repeatback cylinder 39 and the bearings 59, 59" being coaxial. In this construction the shaft 56 is rigid with the piston rod 4|, so that movement of the piston rod causes axial sliding of the shaft 56 along the inner shaft 51.

In operation, if the craft pitches so that the disc 2 controlled b the gyroscope and the pickl. of climb or descent is altered to bring the craft der 39 proportional to of! device 4, 5, 6, 6' takeup a relative position as shown in Figure 1, the valve l2, I3 is operated as already explained so that pressure fluid is supplied to the servomotor to actuate the elevator. As the elevator is moved, air resistance develops, which causes a difference of pressure to develop in the pipes 3|, 33. This difference of pressure is applied by way of the channels 50, ii to the piston 40, resulting in a movement of the piston to the left through a distance determined by this diii'erence of pressure and by the characteristics of the restoring springs 41, 41'. The shaft 56 takes part in this movement and its movement in turn causes the gear sector 54 to turn about the axis 3 thereby moving the follow-up member 5, 6, 6' of the primary controller to follow-up the disc 2 so that the primary controller is restored towards the neutral condition in which the ports 6, 6' are aligned with the edge of the disc 2.

In order to provide an indication of the position of the follow-up member 4', the worm 5B is arranged to mesh not only with the gear segment but also with the pinion H the hub of which is connected by a flexible band 62 to the hub of a drum 63 which carries indications visible in window 64.

A manual control knob 65 is provided on the front of the instrument case to enable the automatic pilot to be set in order to effect a climb or descent of the craft. When this knob ispushed inwards its stem enters further into shaft 51, and a cross-pin 61 carried by it engages in a 'recess in the end of this shaft and at the same sector 54 and pinion 64 to rotate. The position.

of the pick-oil! device 4, 5, 6, 6' at the gyroscope is thus altered whereby the automatic pilot thereafter controls the craft to that new angle/of climb or descent in which the pick-off device is once again in alignment with the disc 2. Spring 68 returns clutch plate 68 into engagement with gear 69 when the manual control knob 65 is released.

' A barometric control device may be added by arranging that it operates by turning the gear 10 meshing with the gear 69, so that the angle to, or maintain it at, a desired height.

It will be clear that,.even if there is leakage past the piston 40, a pressure difference is still maintained between the two sides of the cylinthe pressure-difference in the servo-motor. Thus leakages are not detrimental to the operation of the system if they are not too heavy. This fact enables the piston 40- to be rude an easy flt in the cylinder 39, and

. this, together with the continuous lubrication present, allows friction to be kept to a very low value. The fact that leakage is not detrimental may be used to furnish an adjustment to the apparatus, as will now be described.

A by-pass passage I i isprovided interconnecting the two ends of the repeat-back cylinder 39,

and an adjustable needle valve 12 is provided therein. By adjusting this valve the resistance to the flo'w of fluid by-passing the piston 40 may be adjusted in relation to the resistances to flow in the channels 50 and BI, and in this way a greater or smaller fraction of the difference of ton ll.

pressure effective in the servo-motor it may be made effective in the repeat-back cylinder 38. This provides what is in effect an adjustment of the rudder ratio i. e. of the extent to which is not rigid a in Figure 1, but is a yielding eonu nectlon. The piston III is hollow, the hollow interior itself acting as a cylinder for an inner portion 40'', to which is attached the piston rod II which passes through the end cap 40' of the hollow piston ll and through the end cap I! of the cylinder I! for connection to the shaft It. The interior of the piston III is filled with the same fluid as is used in the cylinder 3!, and the clearances round the inner piston ll" are made so small that this fluid can pass from one side of the piston to the other only very slowly under the forces to which it is subjected in practice.

Subject to this requirement, which will.be defined more precisely below, the inner piston ll" is designed to move as freely as possible i. e. with.

as little friction as possible, in the bore of pis- In this arrangement the pick-off device l at the gyroscope is itself spring-contralised independently of the piston by the following arrangement:

The shaft It is provided with a flange 13 at one end and with a shoulder-13' at the other end; these engage respectively with loose collars 1t, 14'. Collar 14 is guided on pins, of which only two, 1|, 1| are visible in Figure 2, and compression springs, such as 10, 18', actsbetween the collar 14 and the casing to press the collar to the right until it abuts against thestop 11, which surrounds the shaft It. The other collar 14' is forced to the left by the compression spring 1|" until it abuts against the stop 11', which surrounds the shaft II. The parts are so, dimensioned that, when the shaft It is central the oscillation of the craft in the shorter of its periods of oscillation. ,The control system of Figof a slowly yielding member in the repeat-back connection, which is a feature of the present invention. In the form of the invention being described the yield takes place between the piston rod ll and the cylinder ll of a dash-pot. Buch arrangements usually give rise to dimculties in preventing leakage of fluid, but the expedient adopted in Figure 2 of using the cylinder ll of the dash-pot itself as the piston in another cylinder It overcomes these difiiculties and also makes the whole apparatus compact.

In Figure 2 the centralising arrangements for the piston 40' are simpler than those for the piston 40 of Figure 1. They consist of two simple opposed compression springs 18, ll, acting directly between the piston 4| and the end caps 42, 42' of the cylinder 30. This arrangement does not give such precise centering, independent of friction, secular changes in the springs, and so on, as does the arrangement of Figure l, but this fact is not of importance in view of the existence of the independent centralising arrangements for the shaft 50.

Figure 2 also illustrates a number of modifica tions of the arrangements shown in Figure 1-for applying hydraulic pressure to the piston ll. These modifications are,not essentially connected with the use of the yielding connection of collar-s14, 14 rest against the stops 11, 11'. Blight movement of the shaft in either direction I causes the flange 13 or the shoulder 13' to lift the corresponding collar 14 or 14' from its stop 11 or 11' against the return force exerted by the compression springs 1|, 1| or 1|".

It should be noted that, if the attitude set for thecraftisalteredbytm'ningknobllthecentralising springs 1|, 1. or 18" centralise thepick-oi! I to the new position, since the alteration of the attitude is made by altering the relation between, the longitudinal position of the shaftltandthepodtionofthepick ofldevicel.

It can readily be seen that, if the piston ll is displaced; taking with it the piston II", and

shaft It, and causing the pick-o8 l to turn, the

springs 10, 10' (or spring 10") are thereby compressedandexertarestorlngforceonthelhatt BI, which slowly displaces the piston ll" imide the piston ll. The restoring force exerted by' the springs 1', 1| (oi-spring 18'') when the-collar 14 (or 14') is lust-raised from its stop 11 .(or 11') is suiiicient to overcome any friction in the parts moving with the shaft-ll, and the dash-.-

.potformedbytheflnionl l"andflleinterior of listen 0' yield slowly under the force applied orlubsidenceperiodofthisarrangement'should beatleastoftheorderoaandpreferabiyoom Iiderablylongerthamtheperlodofa-complete' toit bythe centralisingsprings. Theyielding Figure 2 between the piston It and the pick-oil device 4, and they may, if desired, be imported directly into the system of Figure 1. The channels II, II in the valve casing it of Figure 1 are replaced by p pe connections 1! 1| which-are connected on the one hand to channels II, II-

leading to ports II, II in the cylinder 3!, and-on the other hand to the pipes 3|, 33. Moreover, the connection of pipe 1! to pipe Ii is made to the section II of the pipe on the servo-motor side of the needle valve 3|, so that the pressure difference applied to the piston 40' corresponds to that developed in the servo-motor I l and is unafi'ected by the adjustment of the valve 88.

and the automatic pilot applies the elevator ccrrecttheattitudamoreelevatorisapplied ing the departure of the craftfrom the attitude than is applied when a proportional type of repeat-back is used, and less elevator is applied (and possibly even reverse or checking sponsive to the pressure in the servo-motor, a

spring centralised bellows device may be used, or a corrugated metal bellows (which provides its own centralising forces). Alternatively in place of the piston and cylinder 40 and 39 there may be employed a vane-motor in which a cylindrical casing provided with radial vanes extending inwards towards the centre contains a rotary member provided with outwardly directed radial vanes forming a number of chambers such that application of a difference of pressure to two or more of such chambers, causes the rotary member to rotate against a spring. Further, as the pressure-responsive device employed in the invention, any other type of fluid rotary motor turning against a spring, may be utilized; It is to be understood that these and other modifications, which become desirable in order to carry the invention into effect under diflerent conditions and requirements which have to be fuifilled, may be employed without departing from the scope of the invention.

What we claim is:

1. In. an automatic pilot for aircraft, the combination with a rudder and a hydraulic servo motor therefor, a position maintaining means, a dually controlled pneumatic controller having, a primary and a follow-back control. producing a signal upon displacement of said controller, the primary control thereof being from said position maintaining means, a pneumatically controlled hydraulic relay valve actuated from said signal admitting throttled hydraulic pressure to said servo motor, a pressure repeat-back device connected to the follow-back control of said controller and constituting the sole follow-backbetween the servo and said controller, said repeat- .back device comprising a spring centralized servo connected hydraulically to said relay valve in parallel with said main servo, whereby a pressure is produced in saidmain servo substantially proportional to the primary displacement of the controller.

2. Objectcontrolling means of the character claimed in claim 1, in which said follow-back device is formed by a closed cylinder having a spring centralized, fluid containing, hollow shuttle piston and a second piston within said hollow piston, said second piston being connected to said follow-back control of said controller.

, ROBERT HAYES NISBET.

WILLIAM GEORGE HARDING. 

